I got to spend a few hours putting the Involve Surround Master SQ through its paces. Here are my thoughts and observations.
Stereo-to-surround upconversion: The best I've heard. Better than the results from a Tate 101A, or any of the common receiver modes (Dolby ProLogic IIx, dts Neo:6, etc.). The front stage was completely seamless. With the competition, sometimes vocals get isolated to the front center. On the Surround Master, it was a seamless front stage with an uncanny illusion of "soundstage depth," something I've never experienced before on my system when listening to stereo material. Listening to Dave Brubeck's "Time Out" (an older recording from 1959) was immersive with a middle-of-the-band effect. Sound quality on that CD bested many newer recordings I've heard.
QS decoding: I tried out the Project 3 test LP, the opening track from Paul Anka's "The Painter," and a QS Vox Box set of George Gershwin. On the Project 3 test record, all sounds were placed correctly in their channels during the test playback. Then in the music portion, instrument placement matched the diagrams in the album sleeve. Separation was clean, with no noticeable "bleed-through" to incorrect channels.
I chose the Paul Anka selection ["(You Bring Out) The Best In Me"] to do a comparison of script-based decoding vs. Involve decoding. The results were similar, but not quite identical. I did notice a little percussion bleed-through to the rear channels in the Involve version that was not present in the script-based decode. However, placement of background singers, instruments, etc. was very similar between the two. I don't know which rendition is more "accurate," but overall, I preferred the sound of the Involve rendition.
The Gershwin Vox Box is more of an "ambient surround" presentation. However, it was still a vast improvement over stereo as the Surround Master created a realistic 3-dimensional concert hall ambience out of the QS-encoded LP. Were it not for the vinyl noise, I would have thought I was listening to a multi-channel SACD.
SQ decoding: I tried out the Columbia introduction to SQ quadraphonic sound LP, then listened to a few cuts from Wendy Carlos's "Switched On Bach," Barbra Streisand's "Stoney End," and Billy Joel's "Piano Man." Again, all sound placement tests put sounds in the correct channels. There is a 360-degree pan effect (narration of "all around ... and around ... and around...") that came off flawlessly, with no perceivable gaps or jumps.
My copies of "Switched on Bach" and "Stoney End" are pretty noisy and beat-up (I got them used, and their previous owners didn't treat the records well). This didn't adversely affect the surround decoding, though the music was noisy or distorted as a result. Again, this was due to the records and not the Surround Master.
The decoding of the Billy Joel at least equaled what I have been able to do with the Adobe Audition scripts that have been posted on this site. However, the convenience of playing back the vinyl through the Surround Master can't be beat. This cuts conversion time by 2/3; on my computer, decoding an album with Audition takes about twice the running time ... and that is after playing back the album into the computer!
So we definitely have a winner for decoding '70s quad material, as well as enhancing stereo to surround. If you have matrix quad albums, getting a Surround Master is a no-brainer. Stereo upconversion is also excellent, but with a caveat (see point #3 below).
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And now some questions and comments that I hope the Involve guys can answer:
1) There are connections for 4-channel or 5-channel output. If I want to do 4.0 upconversions of both SQ and QS, should I be using the 4-channel output jacks? Or use FL, FR, SL, SR from the 5.1 jacks? I read over the manuals and addenda twice but did not fully understand the difference between these two connections, and how the front channels differ. There had been some past discussion about the QS decoding only being in 5.1 and not 4.0. Is that still the case? Or can I decode QS in 4.0 (as it was done in the '70s)?
2) What sampling rate / bit depth are used internally to the Surround Master for digitizing and processing the audio? I usually rip LPs at 96/24, but if the Surround Master works at 48/24, there's no point in doing a 96/24 LP rip. I ask this so I can use the highest bit rate for quality reasons, but not waste space by grabbing higher-resolution samples than the Surround Master can re-output as analog audio.
3) How to improve Surround Master and make it appealing to a broader market? The main thing that is missing is digital audio input and output. Relying upon analog input and output is somewhat obsolete in the current home theater world, which has largely migrated to HDMI for everything (except vinyl). I made the switch to HDMI for all my digital sources in 2009 and haven't looked back, as it combines multi-channel audio and video in ONE cable, and eliminates duplicate investment in multiple high-end D/A stages.
Since the Surround Master can act as a stereo-to-surround box, the ideal for digital stereo sources would be to have digital input and output. This avoids quality loss from extra A/D and D/A conversion steps. It will likely require HDMI (and the accompanying expensive licensing) to get a 4.0 or 5.1 lossless PCM surround signal into a pre/pro (the only surround I've seen carried over Toslink and coax is Dolby Digital and dts).
If I could connect up a Surround Master digitally, in between a CD player and pre/pro, I would use it to enhance all my stereo recordings. But I bought the lower-end Oppo players (without the high-performance analog stage), consciously planning to use them as "transports," and that the digital "sound" comes from the pre/pro.
Also, all home theater receivers apply bass management and room correction in the digital domain. My pre/pro forces me to "direct" mode (no bass management and room correction) when using multi-channel analog inputs.
The upshot is that the peculiarities of multichannel analog input mean I take a hit to sound quality for stereo sources. So where I find the Surround Master most useful is for decoding quad vinyl. Then I have a FLAC file or DVD-A that I can play back in all-digital form, getting the benefits of bass management and room correction.
I'd think perhaps the digital "guts" of the Involve stereo-to-surround processing should be sold/licensed to receiver manufacturers. I'd love to pull up "Involve" modes alongside all those Dolby / dts modes. That would also solve the HDMI / bass management / room correction issues. But I realize receiver manufacturers would probably pay $10-$25 per unit shipped for the firmware. It would take a 20X the sales volume to make the same money, and that's if these big multinational conglomerates even bite in the first place.